The present invention relates to wireless communication systems and methods, in particular, to facsimile communications systems and methods.
Facsimile systems are widely used to transmit images, typically of documents, from one location to another. Conventionally, a document is scanned by a xe2x80x9cfax machinexe2x80x9d to convert it into facsimile data which is then transmitted over a communications channel, typically a voice channel on the Public Switched Telephone Network (PSTN). The document is then reconstructed into hard copy from the transmitted facsimile data by a similar facsimile machine located at the other end of the communications channel.
Standard communications protocols have been developed for transmission of facsimile data. Older analog protocols, such as CCITT Group 1 and Group 2, are now generally obsolete. The digital CCITT Group 3 protocol, widely used by conventional office and home facsimile machines, uses digital modems transmitting digital facsimile data at speeds up to 9600 baud over conventional PSTN telephone lines. The Group 3 protocol includes handshaking and signal quality evaluation features which enable facsimile machines to step down the communication baud rate if the communications channel exhibits poor quality. A CCITT Group 4 protocol has also been established to provide less error-prone communication between facsimile machines over public data networks other than the PSTN.
Because of the increased mobility it offers, cellular radiotelephone technology is increasingly supplanting the PSTN for many communications applications. Mobile cellular radiotelephones are now a common sight in businesses, home, and automotive environments. Personal computers have also been adapted for use with cellular radiotelephone communications systems, exchanging the wireline modem for a similar device acting over a cellular radiotelephone voice or data channel.
Examples of suitable cellular networks which could beneficially be used as an alternative to a PSTN include analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, which have been deployed successfully throughout the world. More recently, digital cellular radiotelephone systems such as that designated as IS-54B (and its successor IS-136) in North America and the pan-European GSM system have also been introduced. These systems, and others, are described, for example, in the book titled Cellular Radio Systems by Balston, et al., published by Artech House, Norwood, Mass., 1993. In addition, satellite based radio communication systems are also being utilized to provide wireless communications in various regions such as the Asian Cellular Satellite System (ACeS) generated by Lockheed Martin Corporation. Furthermore, dual-mode mobile terminals are known which allow a single terminal to access to different networks. For example, an analog/digital dual-mode terminal or a terrestrial/satellite dual-mode terminal may be desirable in various geographic areas to maximize the communications capabilities available to a user.
One obstacle to implementation of facsimile communications over cellular radiotelephone communications systems is the generally lower bandwidth, lower signal quality, and higher communications costs which may be associated with cellular radiotelephone channels in comparison to conventional PSTN channels. One approach to providing more reliable radio transmission of facsimile data using packet data protocols with checking and retransmission features is described in U.S. Pat. No. 5,282,238 to Berland. An approach to sending faxes over analog cellular networks is described in U.S. Pat. No. 5,752,199 to Scott. Each of these approaches proposes ways to improve performance of facsimile transmission when a wireless channel is provided for this purpose.
The IS-136 communication standard, which provides for both analog and digital communication support, specifically supports Group 3 type facsimile transmissions. Under the IS-136 standard, a mobile terminal requesting communication access typically provides the communication network a service code. The service code may, for example, request analog speech, digital speech, analog or digital speech with a specified preference, asynchronous data or Group 3 type facsimile services from the IS-136 network. On receipt of a Group 3 facsimile service code, under the IS-136 standard, the communication system determines if a digital traffic channel is available. If a digital traffic channel is available, the request may be serviced, otherwise the service request is rejected. Accordingly, under the IS-136 standard, facsimile transmission requests will not be supported when no digital traffic channels are available.
In order to provide for the foregoing and other objectives, a method is provided for selecting a channel for transmission of a facsimile utilizing a wireless communication network which has two different channel types available for wireless communications. For example, a network such as an IS-136 protocol network supports both analog and digital wireless communication services. The present invention provides systems and methods which preferentially request one of the service types for a transmission of a facsimile but further provides for use of the alternate service type under conditions where a suitable channel is not available for the preferred facsimile support channel. More particularly, in one embodiment, when digital transmission services are not available, but analog services are available, facsimile transmission is provided over the analog channel rather than denying access to the wireless communication network for transmission of the facsimile.
In one embodiment of the present invention, methods are provided for selecting a channel for transmission of a facsimile. A request is transmitted by a mobile terminal to a wireless communication network having a first and a second channel type requesting a channel for use in transmitting a facsimile. A designation of a channel of the first channel type is received from the wireless communication network if a channel of the first channel type is available and of the second channel type if a channel of the first channel type is not available. The facsimile may then be transmitted on the designated channel. In a particular embodiment, the first channel type is a digital traffic channel and the second channel type is an analog voice channel and the facsimile is a Group 3 type facsimile. The wireless communication network may be a dual analog digital system such as an IS-136 protocol network.
In a further embodiment of the present invention, a facsimile having a first protocol is received for transmission. The facsimile is provided to the designated channel without protocol conversion if the designated channel is the analog voice channel. The protocol of the facsimile is converted to a second protocol and the converted protocol facsimile is provided to the designated channel if the designated channel is the digital traffic channel. The first protocol may be a T.30 protocol and the second protocol may be an IS-135 protocol.
In a system aspect of the present invention, a mobile terminal is provided including a portable housing and a wireless communication circuit in the housing and coupled to a wireless communication network having a first and second channel type. A line interface circuit is also provided in the mobile terminal including a facsimile input port and a protocol conversion circuit having an output connected to the wireless communication circuit. A connection line is provided connected to the wireless communication circuit. In addition, a switch is provided connecting one of an input of the protocol conversion circuit or the connection line to the facsimile input port responsive to a request from the wireless communication circuit. The wireless communication circuit in a particular embodiment includes means for requesting connection of the input of the protocol conversion circuit to the facsimile input port responsive to an indication from the wireless communication network that a channel of the first channel type is available for transmission of the facsimile and for requesting connection of the connection line to the facsimile input port responsive to an indication from the wireless communication network that a channel of the first channel type is not available for transmission of the facsimile. A means for transmitting the facsimile on the wireless communication network over a channel of the first channel type and a channel of the second channel type is also provided.
In another embodiment of the present invention, a channel selection system for transmission of a facsimile is provided including means for receiving the facsimile for transmission and means for requesting from a wireless communication network having a first and a second channel type a channel for use in transmitting the facsimile. The channel selection system further includes means for receiving a designation of a channel of the first channel type from the wireless communication network if a channel of the first channel type is available and of the second channel type if a channel of the first channel type is not available and means for transmitting the facsimile on the designated channel.
In a further aspect of the present invention, a channel selection system is provided for receipt of a facsimile including means for receiving a request from a mobile terminal for a channel to use in transmitting the facsimile. The channel selection system also includes means for transmitting a designation of a channel of a first channel type if a channel of the first channel type is available and of a second channel type if a channel of the first channel type is not available. Corresponding methods are also provided.